Chair back



FIG. 1 is a perspective view of a chair back showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a right side elevational view thereof, the left side being a mirror image of the right side; and,

FIG. 5 is a rear elevational view thereof.

The broken lines showing of the seat and legs of the chair in FIGS. 2, 4 and 5 are for illustrative purposes only and form no part of the claimed design. 

The ornamental design of a chair back, as shown and described. 